Rendering smoke to texture sheet
I have previously developed an add-on to achieve this (Smoke2EXR) for the old smoke simulation (Blender 2.81 and earlier) and am in the process of updating it to work with the new Mantaflow fluid simulation (Fluid2EXR) in Blender 2.82 and later.
The add-on can be downloaded from https://github.com/baldingwizard/Blender-Addons/wiki (click on Fluid2EXR, download the ZIP and use the 'Install..' button in the Add-on Preferences editor to install it).
Once you have run your smoke simulation, save your .blend (important to not lose your work - as well as the add-on needing to save your image 'local' to your Blend file, so it needs to have been saved first). Press F3 to bring up the operator panel and type 'EXR' to find the add-on.

You should now be prompted by the add-on for the frame you wish to convert (it defaults to the current frame) :

Click 'OK' and after a &quot;short&quot; delay (it will take much longer for higher resolution smoke domain) should complete. Note that it can take a long time and will hang Blender while it is running - open the System Console before you run the conversion to be able to monitor progress (it outputs diagnostic messages to the console).
Once complete you should have your smoke domain in a 'spritesheet' format.

Note that in addition to the smoke density it will also extract the Flame, Heat, Color (only useful if you've set the color of your smoke) and Velocity data to separate images.

The filename is based on the domain size (eg, '64') and the 'spritesheet' grid dimensions (eg, '8x8').
I'm currently looking to enhance the building of the images to use Numpy which should hopefully drastically improve performance (it can currently take a very long time to extract a large domain or one with more than a few levels of Noise).